JP3628711B2 - Air data measurement system with circuitry to linearize pressure transducer output - Google Patents

Air data measurement system with circuitry to linearize pressure transducer output Download PDF

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JP3628711B2
JP3628711B2 JP54392698A JP54392698A JP3628711B2 JP 3628711 B2 JP3628711 B2 JP 3628711B2 JP 54392698 A JP54392698 A JP 54392698A JP 54392698 A JP54392698 A JP 54392698A JP 3628711 B2 JP3628711 B2 JP 3628711B2
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JP2002500756A (en
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ヘドリック，ジェオフリイ，エス．，エム．
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イノヴァティヴ ソルーションズ アンド サポート インコーポレーテッド
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P5/00—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft
    • G01P5/14—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring differences of pressure in the fluid
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
    • G01L9/02—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means by making use of variations in ohmic resistance, e.g. of potentiometers, electric circuits therefor, e.g. bridges, amplifiers or signal conditioning
    • G01L9/06—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means by making use of variations in ohmic resistance, e.g. of potentiometers, electric circuits therefor, e.g. bridges, amplifiers or signal conditioning of piezo-resistive devices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P13/00—Indicating or recording presence, absence, or direction, of movement
    • G01P13/02—Indicating direction only, e.g. by weather vane
    • G01P13/025—Indicating direction only, e.g. by weather vane indicating air data, i.e. flight variables of an aircraft, e.g. angle of attack, side slip, shear, yaw
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D1/00—Control of position, course, altitude or attitude of land, water, air or space vehicles, e.g. using automatic pilots
    • G05D1/0055—Control of position, course, altitude or attitude of land, water, air or space vehicles, e.g. using automatic pilots with safety arrangements
    • G05D1/0077—Control of position, course, altitude or attitude of land, water, air or space vehicles, e.g. using automatic pilots with safety arrangements using redundant signals or controls

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Aviation & Aerospace Engineering (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Automation & Control Theory (AREA)
  • Measuring Fluid Pressure (AREA)

Description

発明の背景
1.発明の分野
この発明は、エアデータ測定システムに関し、さらに詳しくは、圧力変換器と、航空機の対気速度に関連して圧力変換器のアナログ出力を線形化する回路とを有するエアデータ測定システムに関する。
2.関連技術の説明
航空機の対気速度を決めるためには、航空機の外側の気流の衝撃圧力Qcを測定する必要がある。衝撃圧力は対気流のトータル又はピトー（Pitot）圧力と静的圧力との間の差として定義される。それは対気速度で指数関数的に変わり、次のごとく表せる；
Qc＝Ps＊(((１＋(0.2＊(As/S)２))3.5)−１)
ここで、Ps＝海上での圧力；
As＝対気速度；及び
Ss＝音速
衝撃圧力は、圧抵抗ブリッジを装着した可撓性ダイアフラムを介して差動圧力変換器によって通常測定される。その変換器は、ダイアフラムの変形に対応して電圧信号を発生すべく形成されている。可撓性ダイアフラムの物理的な変形特性により、圧力変換器はその弾性変形範囲のすみずみの圧力に線形的に比例する電圧信号を作成することができない。従って、製造者は、電圧信号が圧力範囲、すなわちダイアフラムの弾性変形範囲内に相対的に入る圧力範囲に線形的に比例する１つの範囲を特定する。圧力の完全な範囲を正確に測定するためには、ユーザはしばしば異なる線形作動範囲を持つ多数の圧力変換器を用いる。しかしながら、この解決策はエアデータ測定システムのコストと複雑さを増す。
線形の拡張範囲を持つ、すなわち圧力の拡張範囲を越える変形に線形的に関連した電圧信号を発生できる、従来の圧力変換器があるが、それらは高価であり、従って商業用途を限定されている。これらの圧力変換器はまた、オフセット・エラーの大きさが変換器の圧力範囲に直接比例するので、比較的大きなオフセット・エラーを有し好ましくない。さらに、衝撃圧力Ｑが対気速度により指数関数的に変わるので、差動圧力変換器は低い対気速度で低い電圧信号を作成する。これらの低い電圧信号は測定システムのノイズに影響されやすく、それによって低い対気速度の測定を不正確にする。従ってユーザはしばしば高価でかつ高い感度の圧力変換器を低い対気速度範囲用に使用する。
依って、航空機の対気速度の全差動範囲に対する低いコストの圧力変換器を用い、かつ高対気速度のみならず低対気速度に対する高度に正確な圧力測定を提供するエアデータ測定システムが必要である。
発明の要旨
この発明の目的は、単一の圧力変換器を使用する航空機の対気速度の全範囲を越えるエア圧力を正確に測定する低コストのエアデータ測定システムを提供することである。
この発明のもう１つの目的は、単一の圧力変換器を使用する航空機の対気速度の拡張範囲（extended airspeed range）を越えるエア圧力を正確に測定する低コストのエアデータ測定システムを提供することである。
この発明の更にもう１つの目的は、低い対気速度では圧力変換器の感度を自動的に増大させ、高い対気速度では圧力変換器の感度を減じる回路を提供することである。
この発明の更にもう１つの目的は、対気速度の全作動範囲に対して高感度の圧力変換器を用いて変換器のオフセット・エラー（offset error）を最小にできるようにすることである。
好ましい実施態様によれば、エアデータ測定システムは、航空機の外側のエア圧力を感知する装置と、可撓性ダイアフラムに装着された圧抵抗ブリッジ（piezoresistive bridge）を有する圧力変換器とを含む。圧抵抗ブリッジはダイアフラム、従ってブリッジに供給された感知エア圧力に応答して変わる電気抵抗を有する。システムはまた、圧抵抗ブリッジに励起電流を供給しその大きさを変えるために圧力変換器に作動的に接続された電流源を含む。更に含まれるのは、圧抵抗ブリッジの電気抵抗の変化を感知し、感知エア圧力に対応して圧抵抗ブリッジから信号を出力するために、圧力変換器に接続された出力装置である。電流源手段は低対気速度で変換器の感度を増大させ、高対気速度で変換器の感度を減ずるように、出力装置の出力信号に応答してブリッジへの励起電流を変える。
この発明の他の目的及び特徴は、添付の図面に関連して考慮された次の詳細な説明から明らかになろう。しかしながら、その図面は、図示の目的にのみデザインされたものであって、この発明の限定の定義としてではなく、この発明の参照は添付された請求の範囲に対してなされるべきであることを理解されるべきである。
【図面の簡単な説明】
図面において、同様の参照記号は次の数図を通じて類似の要素を示す：
図１は、この発明のエアデータ測定システムの好ましい実施態様を略図で示し、
図２は、この発明の線形化回路の好ましい実施態様の概略図であり；
図３は、図２の線形化回路の実施態様のいくつかのパラメータをグラフで示し；
図４は、この発明のエアデータ測定システムのもう１つの実施態様の回路図である。
現在の好ましい実施態様の詳細な説明
図１を詳細に参照すると、この発明による航空機の対気速度を測定するエアデータ測定システムの現在の好ましい実施態様が示されている。図１を詳細に参照すると、この発明による航空機の対気速度を測定するエアデータ測定システムの現在の好ましい実施態様が示されている。システム10は、航空機の外側の気流の静的およびピトー（又はトータル）圧力P1とP2に連通する一対の圧力ポート（図示しない）に接続された差動圧力変換器14を含む。圧力変換器14は、例えばEGアンドＧ社のICセンサ・型番1210A−002のように、可撓性ダイアフラムと、その電気抵抗が測定圧力（つまりP1とP2の差）によって変化し、かつ、その感度が通過する励起電流（Ix）によって変化する圧抵抗ブリッジとを含むことが好ましい。システム10はまた、圧力変換器14の温度を感知する温度センサ16と、例えば中央処理ユニット（CPU）25による好適なヒータ制御器および特定温度範囲内に圧力変換器14の温度を調整又は維持するヒータ電源に接続されるヒータ18とを含む。参照電圧源22は温度センサ16に電圧信号を供給する。
エアデータ測定システム10は、参照電圧源22から参照電圧信号Vrefを受け取って圧力変換器14への励起電流Ixを生成する線形化回路20を含む。線形化回路20は、変換器14によって感知される衝撃圧力に対応する圧力指示信号Eoutを出力する。システム10はまた、アナログ圧力指示信号Eoutを、CPU25により処理するデジタル信号E'outに変換するアナログ／デジタル変換器24を含んでもよい。CPU25は、E'outを含む多くのパラメータと、温度センサからの温度測定信号（Temp）と、圧力変換器14の温度影響を補正するためのEEROM12からの適当な較正定数とに基づいて、航空機の対気速度を計算する。
以下に述べるように、線形化回路20によって与えられる励起電流Ixは自動的に調整でき、航空機の対気速度に対して変換器の感度を変化させる。この特徴により、航空機の対気速度の全作動範囲用として、ユーザが約2psiつまり４インチHgの小さな線形圧力範囲を有する低価格圧力変換器を使用できることは、好都合である。
図２は圧力変換器14の圧抵抗ブリッジ26と、線形化回路20の好ましい実施態様とを概略的に示す。圧抵抗ブリッジ26は抵抗R1、R2、R3およびR4と接合点28、30、32および34を含む。線形化回路20は、好ましくは、非反転入力38、反転入力40および極めて大きい増幅ゲインK1（これは理想的には無限大であるが、例えば100,000に設定できる）を有するオペアンプ36を含む。非反転入力38は、参照電圧源22に接続されて参照電圧信号Vref（例えば2.5ボルト）を受け、反転入力40は接合点42を介してブリッジ26のノード32へ接続される。アンプ36の出力はブリッジ26のノード28に接続される。感知抵抗Ｒ ｓは、その一端が接合点42に接続され、他端が接地される。回路20はまた、非反転入力46,反転入力48および増幅ゲインK2（例えば、K2＝100）を有する差動アンプ44を含む。非反転入力46はブリッジ26のノード34に接続され、反転入力48はブリッジ26のノード30に接続されて、ノード30と34の電位差に比例し、かつ、ダイアフラムと圧抵抗ブリッジ26とに与えられる圧力に対応する圧力指示信号Eoutを出力する。回路20は、一端が接合点42に他端が差動アンプ44の出力に接続されたフィードバック抵抗Rfさらに含む。
そのように接続されると、当業者であれば直ちに理解することであるが、電圧信号Eoutと、RfとRsの抵抗値とは、ブリッジ26を通過する励起電流Ixの量に影響を及ぼし、それによって、ブリッジ26の感度に影響を及ぼす。実際、励起電流Ixは、圧力指示電圧信号Eoutによって変化し、IxはEout＝０のときに最大となり、その後Eoutが増大するにつれてIxは減少する。これは概念的に次のように説明できる。アンプ36は、接合点42をVrefに保持しようとするとき、接合点42からの電流を感知する。従って、EoutがVrefより小さいとき、Ixの一部は必然的にRfを介して漏れる。そこでRsの両端にVrefを維持するために、アンプ36はブリッジ26を介してIxを増大させねばならず、それによってブリッジ26の感度を増大させる。一方、EoutがVrefより大きい時には、電流は差動アンプ44からRfとRsを介して流れる。この電流Ixに対する要求を減じ、接合点42をVrefに維持する。従って、それに応じてオペアンプ36はブリッジ26を通る電流Ixを減じ、それによって、ブリッジ26の感度を減じる。
この実施態様においては、VrefはEoutの大きさがVrefを超えるときIxの大きさが減少するようなIxを調整するためのしきい値のように見えるかもしれない。Eoutの大きさがVrefより小さくなると、Ixの大きさが増大する。
従って、この発明によれば、線形化回路20は、都合のよいことに、低い対気速度（低いEoutに対応する）においてブリッジ26を通る励起電流Ixを増大させ、それによって低い対気速度における変換器14の感度を増大させる。逆に、線形化回路20が励起電流を減ずる時、高い対気速度（高いEoutに対応する）において変換器14の感度は減少する。
変換器14にそのような調整を与えることは特に利点であるが、それは上述の式で示したように衝撃圧力Qcが航空機の対気速度によって指数関数的に変化するからである。その式により、低い対気速度において、圧力の小さい変化は、指示される対気速度の大きい変化に対応し、一方、高い対気速度においては、圧力の小さい変化は対気速度のきわめて小さい変化に対応する。従って、この発明によれば、線形化回路20は、高測定感度、低い対気速度における精度、および高い対気速度における低測定感度を提供する。
この発明は、航空機の対気速度の全作動範囲用として唯一の低コスト圧力変換器を利用できるエアデータ測定システムを提供する。圧力変換器は狭い特定の線形範囲（例えば２インチHg）を有し、高い可撓性を有するダイヤフラム等により圧力単力単位当たり比較的高い電圧信号を出力することが好ましい。但し、注意すべきことは、選択した変換器は十分に堅牢で、圧力の所定範囲の下で作動したときに永久変形しないことが好ましい。
都合のよいことには、エアデータシステム10による圧力測定の精度と信頼性は少なくとも次の点で従来のシステムより十分に改良されている。（１）その出力が線形化回路によって増幅される高感度変換器の使用による低い対気速度の測定、および（２）圧力変換器の特定の圧力範囲のパーセンテージであるオフセット・エラー（つまり、特定の圧力範囲が小さい程、オフセット・エラーが小さくなる）。
１つの特別な実施態様においては、エアデータシステム10の要素は、次の特定の値を有する。
圧力変換器（14）の線形圧力範囲＝4.072インチHg
圧力変換器出力感度＝0.050VFS（フルスケール）
差動アンプ（44）のゲイン＝100
オペアンプ（36）のゲイン＝100,000
Rsの抵抗値＝3,000Ω
Rfの抵抗値＝3,700Ω
Vref＝2,500V
RfとRsの上記抵抗値は、圧力指示信号Eoutが対気速度の範囲、例えば約０〜約500ノットにわたってほぼ線形化されるように選ばれる。この実施態様の性能は、対気速度（A/S）の関数としての次のパラメータによって立証される。（１）線形化回路20のシステムゲインとして見なすことができる正規化されたゲイン（つまり、Eout/衝撃圧力）対A/S、（２）回路20の線形化アンプ出力（つまり、Eout対A/S）、および（３）衝撃圧力として対気速度の関数として表される、線形化回路20がない場合のアンプ出力（つまり、Qc対A/S）。これらのパラメータは図３のグラフで示される。正規化ゲイン（曲線100）の値は左側の縦軸に沿って示され、線形化アンプの出力（曲線102）と線形化なしのアンプ出力（曲線104）の値は、右側の縦軸に示されている。予想されるように、この実施態様の正規化ゲイン（曲線100）は、低い対気速度で最も高く、高い対気速度で最も低い。さらに、線形化アンプの出力（曲線102）つまりEoutは、対気速度に対してほぼ線形である。一方、線形化なしのアンプ出力を示す曲線104は、対気速度に対して指数関数的に変化し、その値は対気速度の全範囲（端の点を除く）について曲線102の値よりも一貫して低い。
前述の開示から明らかであるが、当業者であれば、対気速度の異なる差動範囲を必要とする商用や軍用など様々な用途に対してRfとRsについて容易に適当な抵抗値を選択して線形化回路20を調整するであろう。
図４はこの発明の好ましい実施態様の回路図である。この実施態様は、圧力変換器14,ヒータ18、温度センサ16、線形化回路20、参照電圧源22,および圧力変換器14用の所定較正定数を有するEEROM12を備える。この実施態様では、抵抗RSとRfは、実質的に同じ物理的特性を有し、RsのRfに対する比が時間の経過やある温度範囲にわたって実質的に同じに維持されるように、同じ抵抗のネットワークRN1によりグループ化されている。
この発明のエアデータ測定システムは、対気速度の測定以外に広い多様な使用用途に適する。エアデータ測定システム10は、例えば、航空機の対気速度の測定の代わりに、航空機の外側の大気圧を測定する静圧変換器のみを採用し、航空機の圧力又は気圧高度を決定するようにしてもよい。
オペアンプ36とフィードバック抵抗Rfの代わりにフィードバック・コントローラ（図示しない）と制御可能電流源（図示しない）を用いることもまた、この発明の範囲内である。フィードバック・コントローラは差動アンプ44の出力と、ブリッジ26へ電流Ixを供給する制御可能電流源とに接続される。フィードバック・コントローラは、デジタル又はアナログでもよく、例えばEoutを一組の所定のしきい値と比較することによってEoutを解析し、制御可能電流源によって出力される適当な励起電流Ix（特定のしきい値に対応する）を決定する。
従って、好ましい実施態様に適用されるこの発明の基本的な新しい特徴が示され、説明され、指摘されたが、説明した装置の形式や詳細およびその動作における種々の省略や代用や変更は、この発明の精神から離れることなく当業者によってなされることは、理解されるであろう。例えば、同じ結果を達成するために実質的に同じ方法で実質的に同じ機能を実行する全ての組み合わせのこれらの要素および／又は方法がこの発明の範囲内にあることは、明白に意図されたものである。従って、この発明は、ここに添付されたクレームの範囲によって示されるようにのみ限定される。 Background of the Invention
1. Field of the Invention The present invention relates to an air data measurement system, and more particularly, a pressure transducer and a circuit for linearizing the analog output of the pressure transducer in relation to the airspeed of the aircraft. The present invention relates to an air data measurement system.
2. Description of Related Art In order to determine the airspeed of an aircraft, it is necessary to measure the impact pressure Qc of the airflow outside the aircraft. Impact pressure is defined as the difference between the total airflow or pitot pressure and static pressure. It varies exponentially with airspeed and can be expressed as:
Qc = Ps * (((1 + (0.2 * (As / S) 2 )) 3.5 ) -1)
Where Ps = pressure at sea;
As = airspeed; and
Ss = Sonic Impact Pressure is usually measured by a differential pressure transducer through a flexible diaphragm fitted with a piezoresistive bridge. The transducer is configured to generate a voltage signal in response to diaphragm deformation. Due to the physical deformation characteristics of the flexible diaphragm, the pressure transducer cannot produce a voltage signal that is linearly proportional to the pressure at every corner of its elastic deformation range. Therefore, the manufacturer specifies one range that is linearly proportional to the pressure range in which the voltage signal falls relatively within the pressure range, ie, the elastic deformation range of the diaphragm. In order to accurately measure the full range of pressure, users often use multiple pressure transducers with different linear operating ranges. However, this solution increases the cost and complexity of the air data measurement system.
There are conventional pressure transducers that have a linear expansion range, ie can generate voltage signals that are linearly related to deformations beyond the pressure expansion range, but they are expensive and therefore have limited commercial use . These pressure transducers are also undesirable because they have a relatively large offset error because the magnitude of the offset error is directly proportional to the pressure range of the transducer. Furthermore, since the impact pressure Q varies exponentially with airspeed, the differential pressure transducer produces a low voltage signal at low airspeed. These low voltage signals are susceptible to measurement system noise, thereby making low airspeed measurements inaccurate. Users therefore often use expensive and sensitive pressure transducers for low airspeed ranges.
Thus, there is an air data measurement system that uses low cost pressure transducers for the full differential range of aircraft airspeeds and provides highly accurate pressure measurements for low airspeeds as well as high airspeeds. is necessary.
SUMMARY OF THE INVENTION An object of the present invention is to provide a low-cost air data measurement system that accurately measures air pressure over the full range of airspeed of an aircraft using a single pressure transducer. It is.
Another object of the present invention is to provide a low cost air data measurement system that accurately measures air pressure beyond the extended airspeed range of an aircraft using a single pressure transducer. That is.
Yet another object of the present invention is to provide a circuit that automatically increases the sensitivity of the pressure transducer at low airspeeds and decreases the sensitivity of the pressure transducer at high airspeeds.
Yet another object of the present invention is to use a pressure transducer that is sensitive to the full operating range of airspeed to minimize the offset error of the transducer.
According to a preferred embodiment, the air data measurement system includes a device for sensing air pressure outside the aircraft and a pressure transducer having a piezoresistive bridge mounted on a flexible diaphragm. The piezoresistive bridge has a diaphragm and thus an electrical resistance that changes in response to sensed air pressure supplied to the bridge. The system also includes a current source operatively connected to the pressure transducer to supply an excitation current to the piezoresistive bridge and change its magnitude. Also included is an output device connected to the pressure transducer for sensing a change in electrical resistance of the piezoresistive bridge and outputting a signal from the piezoresistive bridge in response to the sensed air pressure. The current source means changes the excitation current to the bridge in response to the output signal of the output device so as to increase the sensitivity of the transducer at a low airspeed and decrease the sensitivity of the converter at a high airspeed.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. However, the drawings are designed for illustration purposes only and are not intended as a definition of the limits of the invention, but that reference should be made to the appended claims. Should be understood.
[Brief description of the drawings]
In the drawings, like reference characters indicate like elements throughout the following several views:
FIG. 1 schematically illustrates a preferred embodiment of the air data measurement system of the present invention,
FIG. 2 is a schematic diagram of a preferred embodiment of the linearization circuit of the present invention;
FIG. 3 graphically illustrates some parameters of the linearization circuit embodiment of FIG. 2;
FIG. 4 is a circuit diagram of another embodiment of the air data measurement system of the present invention.
Detailed description of the presently preferred embodiment Referring to FIG. 1 in detail, a presently preferred embodiment of an air data measurement system for measuring airspeed of an aircraft according to the present invention is shown. Referring to FIG. 1 in detail, a presently preferred embodiment of an air data measurement system for measuring the airspeed of an aircraft according to the present invention is shown. System 10 includes a differential pressure transducer 14 connected to a pair of pressure ports (not shown) in communication with static and pitot (or total) pressures P 1 and P 2 of the airflow outside the aircraft. Pressure transducer 14, for example, as EG & G Inc., IC sensor Part No. 1210A-002, a flexible diaphragm, the electric resistance varies with the measured pressure (i.e. the difference between P 1 and P 2), and And a piezoresistive bridge whose sensitivity varies with the passing excitation current (I x ). The system 10 also adjusts or maintains the temperature of the pressure transducer 14 within a specific temperature range and a temperature sensor 16 that senses the temperature of the pressure transducer 14 and a suitable heater controller, for example, by a central processing unit (CPU) 25. And a heater 18 connected to the heater power supply. The reference voltage source 22 supplies a voltage signal to the temperature sensor 16.
The air data measurement system 10 includes a linearization circuit 20 that receives a reference voltage signal V ref from a reference voltage source 22 and generates an excitation current I x to the pressure transducer 14. The linearization circuit 20 outputs a pressure indication signal E out corresponding to the impact pressure sensed by the transducer 14. The system 10 may also include an analog / digital converter 24 that converts the analog pressure indication signal E out into a digital signal E ′ out for processing by the CPU 25. CPU25 based many parameters including E 'out, the temperature measurement signal from the temperature sensor (Temp), in a suitable calibration constants from EEROM12 for correcting the temperature effects of the pressure transducer 14, an aircraft Calculate the airspeed.
As described below, the excitation current I x provided by the linearization circuit 20 can be automatically adjusted, changing the sensitivity of the transducer to the airspeed of the aircraft. This feature advantageously allows the user to use a low cost pressure transducer with a small linear pressure range of about 2 psi or 4 inches Hg for the full operating range of the airspeed of the aircraft.
FIG. 2 schematically illustrates the piezoresistive bridge 26 of the pressure transducer 14 and the preferred embodiment of the linearization circuit 20. Piezoresistive bridge 26 includes resistors R 1 , R 2 , R 3 and R 4 and junctions 28, 30, 32 and 34. The linearization circuit 20 preferably includes an operational amplifier 36 having a non-inverting input 38, an inverting input 40, and a very large amplification gain K 1 (which is ideally infinite but can be set to 100,000, for example). Non-inverting input 38 is connected to reference voltage source 22 to receive a reference voltage signal V ref (eg, 2.5 volts), and inverting input 40 is connected to node 32 of bridge 26 via junction 42. The output of the amplifier 36 is connected to the node 28 of the bridge 26. Sensing resistor R s has one end connected to the junction 42, the other end is grounded. The circuit 20 also includes a differential amplifier 44 having a non-inverting input 46, an inverting input 48, and an amplification gain K 2 (eg, K 2 = 100). The non-inverting input 46 is connected to the node 34 of the bridge 26, and the inverting input 48 is connected to the node 30 of the bridge 26, which is proportional to the potential difference between the nodes 30 and 34 and is applied to the diaphragm and the piezoresistive bridge 26. The pressure instruction signal Eout corresponding to the pressure is output. The circuit 20 further includes a feedback resistor R f having one end connected to the junction 42 and the other end connected to the output of the differential amplifier 44.
When so connected, those skilled in the art will immediately understand that the voltage signal E out and the resistance values of R f and R s depend on the amount of excitation current I x passing through the bridge 26. Affects the sensitivity of the bridge 26. In fact, the excitation current I x varies with the pressure indicating voltage signal E out , I x becomes maximum when E out = 0, and then I x decreases as E out increases. This can be explained conceptually as follows. The amplifier 36 senses the current from the junction 42 when trying to hold the junction 42 at Vref . Thus, when E out is less than V ref , a portion of I x inevitably leaks through R f . So in order to maintain V ref across R s , amplifier 36 must increase I x through bridge 26, thereby increasing the sensitivity of bridge 26. On the other hand, when E out is larger than V ref , current flows from the differential amplifier 44 via R f and R s . This requirement for current I x is reduced and junction 42 is maintained at V ref . Thus, the operational amplifier 36 accordingly will reduce the current I x through bridge 26, thereby reducing the sensitivity of the bridge 26.
In this embodiment, V ref may look like a threshold for adjusting I x such that the magnitude of I x decreases when the magnitude of E out exceeds V ref . When the size of E out becomes smaller than V ref , the size of I x increases.
Therefore, according to the present invention, the linearization circuit 20 is, advantageously, increases the excitation current Ix through the bridge 26 at low airspeed (corresponding to a low E out), a low airspeed thereby Increase the sensitivity of the transducer 14 at. Conversely, when the linearization circuit 20 reduces the excitation current, the sensitivity of the transducer 14 decreases at high airspeeds (corresponding to high Eout ).
It is particularly advantageous to provide such adjustment to the transducer 14, it is because the impact pressure Q c as shown in the above equations changes exponentially by airspeed of the aircraft. The equation shows that at low airspeeds, small changes in pressure correspond to large changes in directed airspeed, while at high airspeeds, small changes in pressure are very small changes in airspeed. Corresponding to Thus, according to the present invention, linearization circuit 20 provides high measurement sensitivity, accuracy at low airspeeds, and low measurement sensitivity at high airspeeds.
The present invention provides an air data measurement system that can utilize the only low cost pressure transducer for the entire operating range of airspeed of an aircraft. The pressure transducer has a narrow specific linear range (eg 2 inches Hg) and preferably outputs a relatively high voltage signal per pressure unit, such as by a highly flexible diaphragm. However, it should be noted that the selected transducer is preferably sufficiently robust so that it does not permanently deform when operated under a predetermined range of pressures.
Conveniently, the accuracy and reliability of the pressure measurement by the air data system 10 is sufficiently improved over conventional systems at least in the following respects. (1) low airspeed measurement by use of a high sensitivity transducer whose output is amplified by a linearization circuit, and (2) an offset error that is a percentage of a specific pressure range of the pressure transducer (ie, specific The smaller the pressure range, the smaller the offset error).
In one particular embodiment, the elements of the air data system 10 have the following specific values:
Pressure transducer (14) linear pressure range = 4.072 inches Hg
Pressure transducer output sensitivity = 0.050VFS (full scale)
Gain of differential amplifier (44) = 100
Op amp (36) gain = 100,000
R s resistance = 3,000Ω
R f resistance = 3,700Ω
V ref = 2,500V
The resistance values of R f and R s are selected such that the pressure indication signal E out is approximately linearized over an airspeed range, for example, about 0 to about 500 knots. The performance of this embodiment is demonstrated by the following parameters as a function of airspeed (A / S). (1) Normalized gain (ie, E out / impact pressure) vs. A / S that can be considered as the system gain of the linearization circuit 20 (2) Linearization amplifier output of the circuit 20 (ie, E out vs. A / S), and (3) the amplifier output in the absence of the linearization circuit 20, expressed as a function of airspeed as the impact pressure (ie, Qc vs. A / S). These parameters are shown in the graph of FIG. Normalized gain (curve 100) values are shown along the left vertical axis, and linearized amplifier output (curve 102) and unlinearized amplifier output (curve 104) values are shown on the right vertical axis. Has been. As expected, the normalized gain (curve 100) for this embodiment is highest at low airspeed and lowest at high airspeed. In addition, the output of the linearizing amplifier (curve 102) or E out is approximately linear with airspeed. On the other hand, the curve 104 showing the amplifier output without linearization changes exponentially with respect to the airspeed, and its value is larger than the value of the curve 102 for the entire airspeed range (excluding the end points). Consistently low.
As is apparent from the foregoing disclosure, those skilled in the art can easily determine appropriate resistance values for R f and R s for various applications such as commercial and military applications that require differential ranges with different airspeeds. Select to adjust the linearization circuit 20.
FIG. 4 is a circuit diagram of a preferred embodiment of the present invention. This embodiment comprises a pressure transducer 14, a heater 18, a temperature sensor 16, a linearization circuit 20, a reference voltage source 22, and an EEROM 12 having predetermined calibration constants for the pressure transducer 14. In this embodiment, the resistor R S and R f are, have substantially the same physical properties, as the ratio R f of R s is substantially the same maintained over the course or range of temperatures of time Grouped by the same resistance network RN1.
The air data measurement system of the present invention is suitable for a wide variety of uses other than the measurement of airspeed. The air data measurement system 10 employs, for example, only a static pressure transducer that measures the atmospheric pressure outside the aircraft, instead of measuring the airspeed of the aircraft, and determines the pressure or altitude of the aircraft. Also good.
It is also within the scope of the present invention to use a feedback controller (not shown) and a controllable current source (not shown) in place of operational amplifier 36 and feedback resistor Rf . The feedback controller is connected to the output of differential amplifier 44 and to a controllable current source that supplies current I x to bridge 26. Feedback controller may be a digital or analog, such as E out analyzes E out by comparing with a set of predetermined threshold, the controllable current source appropriate excitation current output by the I x (specific Corresponding to the threshold value).
Accordingly, while the basic new features of the present invention as applied to the preferred embodiment have been shown, described and pointed out, various omissions, substitutions and changes in the form and details of the apparatus described and its operation are intended. It will be understood that those skilled in the art will do without departing from the spirit of the invention. For example, it is expressly intended that all combinations of these elements and / or methods that perform substantially the same function in substantially the same way to achieve the same result are within the scope of the invention. Is. Accordingly, the invention is limited only as indicated by the scope of the claims appended hereto.

Claims (6)

航空機の外側のエア圧力を感知する手段と；
前記感知手段からの感知エア圧力に連通して圧抵抗ブリッジを含み、前記圧抵抗ブリッジが、上流端および下流 端と、これらの上流端および下流端の間に延びる第１お よび第２抵抗分枝部とを有し、各第１および第２抵抗分 枝部が感知エア圧力に応答して変わる電気抵抗を持ち、 さらに分岐点を持つ圧力変換器と；
前記圧抵抗ブリッジの上流端および下流端にそれぞれ作 動的に接続され、前記圧抵抗ブリッジに励起電流を供給しその大きさを変える出力端および入力端を有する励起電流源手段と；
前記圧抵抗ブリッジの前記第１および第２抵抗分枝部の 分岐点の少なくとも一つに接続され、前記圧抵抗ブリッジの電気抵抗の変化を感知する入力端を持ち、さらに感 知エア圧力に対応する出力信号を生じさせる出力端を含 む出力手段と、
前記励起電流源手段の入力端と前記出力手段の出力端と に接続され、前記励起電流源手段が、前記出力信号の大 きさが予め選択された値以下のときには前記圧抵抗ブリ ッジへの前記励起電流を増大させ、前記出力信号の大き さが予め選択された値以上のときには前記圧抵抗ブリッ ジへの前記励起電流を減少させるフィードバック手段と
を備えた航空機用エアデータ測定システム。Means for sensing air pressure outside the aircraft;
Includes a communication with pressure resistance bridge to sense air pressure from the sensing means, the pressure resistance bridge, and the upstream end and a downstream end, first contact and the second resistor-extending between these upstream and downstream ends A pressure transducer having a branch point , each first and second resistance branch having an electrical resistance that changes in response to sensed air pressure; and a branch point ;
Wherein the pressure resistance bridge each work dynamically connected to an upstream end and a downstream end of an excitation current source means having an output end and an input end for changing the size by supplying an excitation current to the piezoresistive bridge;
Connected to said at least one branch point of the first and second resistive branch of the pressure resistance bridge, having an input terminal for sensing a change in electrical resistance of the piezoresistive bridge, further correspond to sensitive intellectual air pressure and including output means an output terminal producing an output signal,
Connected to said input end of the excitation current source means and the output terminal of the output means, the excitation current source means, when the atmosphere of the output signal is less than the preselected value to the piezoresistive bridge the excitation current increase of the when the magnitude of the output signal is above a preselected value and the feedback means for reducing the excitation current to the piezoresistive bridge
Air data measurement system for aircraft equipped with . 前記感知エア圧力が、ピトー圧と静的圧力との差である請求の範囲１のエアデータ測定システム。The air data measurement system according to claim 1, wherein the sensed air pressure is a difference between a Pitot pressure and a static pressure. 前記出力手段が、出力、反転入力及び非反転入力を有する差動アンプと、前記差動アンプが感知エア圧力に対応して電圧信号を出力するように、前記差動 アンプの前記反転入力及び非反転入力を前記圧抵抗ブリ ッジの前記分岐点に接続する手段とを含む請求の範囲１のエアデータ測定システム。Said output means, output, and the differential amplifier having an inverting input and non-inverting input such that said differential amplifier outputs a voltage signal corresponding to the sensed air pressure, the inverting input and the non of the differential amplifier air data measurement system according to claim 1 including means for connecting the inverting input to the branch point of the pressure resistance bridge. 前記励起電流源手段が、
参照電圧信号を供給する手段と；
出力と、反転及び非反転入力とを有するオペアンプであって、前記非反転入力を前記参照電圧供給手段に接続す る手段と、前記反転入力を前記圧抵抗ブリッジの下流端 に接続する手段と、前記オペアンプの出力を前記圧抵抗 ブリッジの下流端に接続する手段とを有し、さらに反転及び非反転入力が実質的に同一電圧となるように極めて大きなゲインを有するオペアンプとを含み；
前記フィードバック手段が、
第１端及び第２端を有する感知抵抗であって、前記感知 抵抗の第１端を前記圧抵抗ブリッジの下流端及び前記オペアンプの前記反転入力に接続する手段を有する感知抵 抗と、
励起電流が前記圧抵抗ブリッジの上流端から下流端に流 れるように前記感知抵抗の第２端を接地に接続する手段 と；
前記差動アンプの前記出力に接続された第１端と、前記 オペアンプからの励起電流が前記差動アンプの前記出力に応答して変わるように前記感知抵抗の前記第１端に接続された第２端とを有するフィードバック抵抗とを含む
請求の範囲４のエアデータ測定システム。The excitation current source means comprises:
Means for providing a reference voltage signal;
An output, and means comprising an operational amplifier having an inverting and non-inverting input, connecting means to connect the non-inverting input to the reference voltage supply means, the inverting input to the downstream end of the pressure resistance bridge, Means for connecting the output of the operational amplifier to the downstream end of the piezoresistive bridge, and further comprising an operational amplifier having a very large gain so that the inverting and non-inverting inputs have substantially the same voltage ;
The feedback means comprises :
A sensing resistor having a first end and a second end, a sensing resistor having a means for connecting the first end of the sensing resistor to the inverting input of the downstream end and the operational amplifier of the pressure resistance bridge,
Means for exciting current is connected to the ground the second end of the sensing resistor as a flow from the upstream end to the downstream end of the pressure resistance bridge;
A first end connected to said output of said differential amplifier, the excitation current from the operational amplifier is connected to the first end of the sense resistor to vary in response to the output of the differential amplifier The air data measurement system of claim 4 including a feedback resistor having two ends. 前記励起電流源手段が参照電圧を持ち、前The excitation current source means has a reference voltage, 記出力信号の予め選択された値がその参照電圧に等しいThe preselected value of the output signal is equal to its reference voltage 請求の範囲１のエアデータ測定システム。The air data measurement system according to claim 1. 予め選択された参照電圧を提供する参照電圧源と；
エア圧力を感知する圧抵抗ブリッジを含む圧力変換器で あって、前記圧抵抗ブリッジが、上流端および下流端と これらの上流端および下流端の間に延びる第１および第 ２抵抗分枝部とを有し、これらの第１および第２抵抗分 枝部のそれぞれが前記感知エア圧力により変わる電気抵 抗を持ち、さらに分岐点を持つ圧力変換器と；
前記圧抵抗ブリッジへの励起電流を発生させるオペアン プであって、出力と、反転及び非反転入力と、この非反 転入力を前記参照電圧源に接続する手段と、前記オペア ンプの出力を前記圧抵抗ブリッジの上流端に接続する手 段とを有し、さらに反転及び非反転入力が実質的に同一の電圧になるように極めて大きなゲインを有するオペアンプと；
出力と、反転及び非反転入力とを有する差動アンプであって、前記差動アンプの前記反転及び非反転入力を前記 圧抵抗ブリッジの分岐点に接続する手段を有し、さらに前記圧抵抗ブリッジの電気抵抗の変化に対応して出力信 号を発生させる差動アンプと；
第１端及び第２端を有する感知抵抗であって、前記感知 抵抗の第１端を前記圧抵抗ブリッジの下流端と前記オペアンプの前記反転入力とに接続する手段と、前記感知抵 抗の前記第２端を接地に接続する手段とをさらに有する感知抵抗と；
第１端及び第２端を有するフィードバック抵抗であって、前記フィードバック抵抗の第１端を前記差動アンプ の前記出力に接続する手段と、前記オペアンプから前記 圧抵抗ブリッジの上流端への励起電流が前記作動アンプの前記出力信号により変わるように、前記フィードバッ ク抵抗の第２端を前記感知抵抗の第１端に接続する手段 とをさらに有するフィードバック抵抗と
からなる、圧力変換器の出力を線形化する回路。 A reference voltage source providing a preselected reference voltage;
A pressure transducer including a piezoresistive bridge for sensing air pressure , wherein the piezoresistive bridge includes upstream and downstream ends and first and second resistance branches extending between the upstream and downstream ends. the a, has an electrical resistance of each of the first and second resistive branch portion thereof is changed by said sensing air pressure, and further pressure transducer with a branching point;
A op amp Ru generates an excitation current to the pressure resistance bridge, an output, an inverting and non-inverting inputs, means for connecting the non-inverting input to the reference voltage source, the output of the op amp and a means to connect to the upstream end of the pressure resistance bridge, an operational amplifier further having an inverting and a very large gain as the non-inverting input is substantially the same voltage;
A differential amplifier having an output and an inverting and non -inverting input , comprising means for connecting the inverting and non-inverting inputs of the differential amplifier to a branch point of the piezoresistive bridge; in response to a change in the electrical resistance of the differential amplifier for generating an output signal;
A sensing resistor having a first end and a second end, means for connecting the first end of the sensing resistor and the inverting input of said operational amplifier and a downstream end of the pressure resistance bridge, the said sensing resistor A sensing resistor further comprising means for connecting the second end to ground ;
A feedback resistor having a first end and a second end, the means for connecting the first end of the feedback resistor to the output of the differential amplifier ; and an excitation current from the operational amplifier to the upstream end of the piezoresistive bridge as but vary by the output signal of the operation amplifier, consisting of a feedback resistor and further comprising a means for connecting the second end of the feedback resistor to the first end of the sensing resistor, the output of the pressure transducer Circuit to linearize.
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WO1998041911A1 (en) 1998-09-24
WO1998047008A2 (en) 1998-10-22
US5946642A (en) 1999-08-31
EP0988630A4 (en) 2006-01-18
JP2002500756A (en) 2002-01-08
WO1998047008A3 (en) 1999-02-25
EP0988630A2 (en) 2000-03-29

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